This study —the largest of its kind so far— has assessed the in-situ energy efficiency of over 1,000 residential heat pump systems across Central Europe, providing valuable insights for the construction sector. Conducted over a two-year period, the research applies previously lab-based methodologies to real-world conditions, offering a clearer picture of system performance post-installation.

The findings indicate that 17% of air-source heat pumps and 2% of ground-source systems fail to achieve their expected efficiency levels. Additionally, around 10% of the systems analysed were oversized for their intended application, while 1% were undersized—both scenarios with implications for energy use and operational costs.

This study highlights the need for standardised checks after installation and digital tools that offer clear, practical advice. These improvements can help homeowners and installers optimise performance, reduce energy consumption, and lower costs.